Researchers Develop Open Accumulator to Store Off-Shore Wind-Power Energy
Researchers affiliated with the Center for Compact and Efficient Fluid Power (CCEFP), an NSF-funded Engineering Research Center (ERC) headquartered at the University of Minnesota, are developing a fluid-power-based approach to storing wind energy. This work, which is being accomplished with a four-year, $2 million research grant from the NSF's Engineering Frontiers for Research and Innovation (EFRI) program, enables extending research efforts into an application area with high power and weight levels by using a multi-disciplinary, multi-university team drawing on the open accumulator energy-storage concept already developed in the ERC.
Wind power is intermittent and unpredictable; it is also generally more abundant during nighttime hours when demand is low. Therefore, the ability to store wind power can significantly increase the usefulness, predictability, and availability of this renewable and clean energy source. For off-shore wind farms, where transmission and connections are more costly, localized energy storage can also increase the annual energy output of these electrical infrastructure elements. However, storing large amounts of energy (on the order of several MW-hrs) economically, efficiently, and with the capability of high conversion rates (at several MWs) is a challenge. The open-accumulator concept addresses this challenge.
The open-accumulator concept is to store excess wind energy as high-pressure compressed air in pressure vessels at or near the wind turbine. (See accompanying figure.) The compressed air is then released to generate electricity when the instantaneous wind power is not sufficient to meet current power demand. In this way, power output from the wind turbine will be more predictable and steady, and energy that would otherwise be wasted will be captured. Also, because energy storage occurs prior to generation of electricity, many electrical components can be downsized. By enhancing heat transfer inside the air compressor/expander, a near-isothermal process is achieved, thus attaining high efficiency.